On average, life satisfaction is mildly decreasing up to age fifty-five followed by a hump shape with a maximum at seventy. The analysis at the lower levels suggests that people differ in their life satisfaction trends, whereas the hump shape after age fifty-five is robust. No important differences between men and women are found. In contrast, education groups differ in their trends: highly educated people become happier over the life cycle, where life satisfaction decreases for less educated people. Source (Baetschmann, May 2012).
I have seen several articles reaching similar conclusions (see here). Even considering these results I would like to think that there is room for "entrepreneurial happiness" throughout one's life."
HT: Clarence Nkengne Tsimpo.